1//===--- ExprClassification.cpp - Expression AST Node Implementation ------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements Expr::classify.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/AST/Expr.h"
15#include "clang/AST/ASTContext.h"
16#include "clang/AST/DeclCXX.h"
17#include "clang/AST/DeclObjC.h"
18#include "clang/AST/DeclTemplate.h"
19#include "clang/AST/ExprCXX.h"
20#include "clang/AST/ExprObjC.h"
21#include "llvm/Support/ErrorHandling.h"
22using namespace clang;
23
24typedef Expr::Classification Cl;
25
26static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);
27static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);
28static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T);
29static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);
30static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E);
31static Cl::Kinds ClassifyConditional(ASTContext &Ctx,
32                                     const Expr *trueExpr,
33                                     const Expr *falseExpr);
34static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
35                                       Cl::Kinds Kind, SourceLocation &Loc);
36
37Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
38  assert(!TR->isReferenceType() && "Expressions can't have reference type.");
39
40  Cl::Kinds kind = ClassifyInternal(Ctx, this);
41  // C99 6.3.2.1: An lvalue is an expression with an object type or an
42  //   incomplete type other than void.
43  if (!Ctx.getLangOpts().CPlusPlus) {
44    // Thus, no functions.
45    if (TR->isFunctionType() || TR == Ctx.OverloadTy)
46      kind = Cl::CL_Function;
47    // No void either, but qualified void is OK because it is "other than void".
48    // Void "lvalues" are classified as addressable void values, which are void
49    // expressions whose address can be taken.
50    else if (TR->isVoidType() && !TR.hasQualifiers())
51      kind = (kind == Cl::CL_LValue ? Cl::CL_AddressableVoid : Cl::CL_Void);
52  }
53
54  // Enable this assertion for testing.
55  switch (kind) {
56  case Cl::CL_LValue: assert(getValueKind() == VK_LValue); break;
57  case Cl::CL_XValue: assert(getValueKind() == VK_XValue); break;
58  case Cl::CL_Function:
59  case Cl::CL_Void:
60  case Cl::CL_AddressableVoid:
61  case Cl::CL_DuplicateVectorComponents:
62  case Cl::CL_MemberFunction:
63  case Cl::CL_SubObjCPropertySetting:
64  case Cl::CL_ClassTemporary:
65  case Cl::CL_ArrayTemporary:
66  case Cl::CL_ObjCMessageRValue:
67  case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break;
68  }
69
70  Cl::ModifiableType modifiable = Cl::CM_Untested;
71  if (Loc)
72    modifiable = IsModifiable(Ctx, this, kind, *Loc);
73  return Classification(kind, modifiable);
74}
75
76/// Classify an expression which creates a temporary, based on its type.
77static Cl::Kinds ClassifyTemporary(QualType T) {
78  if (T->isRecordType())
79    return Cl::CL_ClassTemporary;
80  if (T->isArrayType())
81    return Cl::CL_ArrayTemporary;
82
83  // No special classification: these don't behave differently from normal
84  // prvalues.
85  return Cl::CL_PRValue;
86}
87
88static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang,
89                                       const Expr *E,
90                                       ExprValueKind Kind) {
91  switch (Kind) {
92  case VK_RValue:
93    return Lang.CPlusPlus ? ClassifyTemporary(E->getType()) : Cl::CL_PRValue;
94  case VK_LValue:
95    return Cl::CL_LValue;
96  case VK_XValue:
97    return Cl::CL_XValue;
98  }
99  llvm_unreachable("Invalid value category of implicit cast.");
100}
101
102static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
103  // This function takes the first stab at classifying expressions.
104  const LangOptions &Lang = Ctx.getLangOpts();
105
106  switch (E->getStmtClass()) {
107  case Stmt::NoStmtClass:
108#define ABSTRACT_STMT(Kind)
109#define STMT(Kind, Base) case Expr::Kind##Class:
110#define EXPR(Kind, Base)
111#include "clang/AST/StmtNodes.inc"
112    llvm_unreachable("cannot classify a statement");
113
114    // First come the expressions that are always lvalues, unconditionally.
115  case Expr::ObjCIsaExprClass:
116    // C++ [expr.prim.general]p1: A string literal is an lvalue.
117  case Expr::StringLiteralClass:
118    // @encode is equivalent to its string
119  case Expr::ObjCEncodeExprClass:
120    // __func__ and friends are too.
121  case Expr::PredefinedExprClass:
122    // Property references are lvalues
123  case Expr::ObjCSubscriptRefExprClass:
124  case Expr::ObjCPropertyRefExprClass:
125    // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
126  case Expr::CXXTypeidExprClass:
127    // Unresolved lookups get classified as lvalues.
128    // FIXME: Is this wise? Should they get their own kind?
129  case Expr::UnresolvedLookupExprClass:
130  case Expr::UnresolvedMemberExprClass:
131  case Expr::CXXDependentScopeMemberExprClass:
132  case Expr::DependentScopeDeclRefExprClass:
133    // ObjC instance variables are lvalues
134    // FIXME: ObjC++0x might have different rules
135  case Expr::ObjCIvarRefExprClass:
136  case Expr::FunctionParmPackExprClass:
137  case Expr::MSPropertyRefExprClass:
138    return Cl::CL_LValue;
139
140    // C99 6.5.2.5p5 says that compound literals are lvalues.
141    // In C++, they're prvalue temporaries.
142  case Expr::CompoundLiteralExprClass:
143    return Ctx.getLangOpts().CPlusPlus ? ClassifyTemporary(E->getType())
144                                       : Cl::CL_LValue;
145
146    // Expressions that are prvalues.
147  case Expr::CXXBoolLiteralExprClass:
148  case Expr::CXXPseudoDestructorExprClass:
149  case Expr::UnaryExprOrTypeTraitExprClass:
150  case Expr::CXXNewExprClass:
151  case Expr::CXXThisExprClass:
152  case Expr::CXXNullPtrLiteralExprClass:
153  case Expr::ImaginaryLiteralClass:
154  case Expr::GNUNullExprClass:
155  case Expr::OffsetOfExprClass:
156  case Expr::CXXThrowExprClass:
157  case Expr::ShuffleVectorExprClass:
158  case Expr::IntegerLiteralClass:
159  case Expr::CharacterLiteralClass:
160  case Expr::AddrLabelExprClass:
161  case Expr::CXXDeleteExprClass:
162  case Expr::ImplicitValueInitExprClass:
163  case Expr::BlockExprClass:
164  case Expr::FloatingLiteralClass:
165  case Expr::CXXNoexceptExprClass:
166  case Expr::CXXScalarValueInitExprClass:
167  case Expr::UnaryTypeTraitExprClass:
168  case Expr::BinaryTypeTraitExprClass:
169  case Expr::TypeTraitExprClass:
170  case Expr::ArrayTypeTraitExprClass:
171  case Expr::ExpressionTraitExprClass:
172  case Expr::ObjCSelectorExprClass:
173  case Expr::ObjCProtocolExprClass:
174  case Expr::ObjCStringLiteralClass:
175  case Expr::ObjCBoxedExprClass:
176  case Expr::ObjCArrayLiteralClass:
177  case Expr::ObjCDictionaryLiteralClass:
178  case Expr::ObjCBoolLiteralExprClass:
179  case Expr::ParenListExprClass:
180  case Expr::SizeOfPackExprClass:
181  case Expr::SubstNonTypeTemplateParmPackExprClass:
182  case Expr::AsTypeExprClass:
183  case Expr::ObjCIndirectCopyRestoreExprClass:
184  case Expr::AtomicExprClass:
185    return Cl::CL_PRValue;
186
187    // Next come the complicated cases.
188  case Expr::SubstNonTypeTemplateParmExprClass:
189    return ClassifyInternal(Ctx,
190                 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
191
192    // C++ [expr.sub]p1: The result is an lvalue of type "T".
193    // However, subscripting vector types is more like member access.
194  case Expr::ArraySubscriptExprClass:
195    if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
196      return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
197    return Cl::CL_LValue;
198
199    // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
200    //   function or variable and a prvalue otherwise.
201  case Expr::DeclRefExprClass:
202    if (E->getType() == Ctx.UnknownAnyTy)
203      return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
204               ? Cl::CL_PRValue : Cl::CL_LValue;
205    return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
206
207    // Member access is complex.
208  case Expr::MemberExprClass:
209    return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
210
211  case Expr::UnaryOperatorClass:
212    switch (cast<UnaryOperator>(E)->getOpcode()) {
213      // C++ [expr.unary.op]p1: The unary * operator performs indirection:
214      //   [...] the result is an lvalue referring to the object or function
215      //   to which the expression points.
216    case UO_Deref:
217      return Cl::CL_LValue;
218
219      // GNU extensions, simply look through them.
220    case UO_Extension:
221      return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
222
223    // Treat _Real and _Imag basically as if they were member
224    // expressions:  l-value only if the operand is a true l-value.
225    case UO_Real:
226    case UO_Imag: {
227      const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
228      Cl::Kinds K = ClassifyInternal(Ctx, Op);
229      if (K != Cl::CL_LValue) return K;
230
231      if (isa<ObjCPropertyRefExpr>(Op))
232        return Cl::CL_SubObjCPropertySetting;
233      return Cl::CL_LValue;
234    }
235
236      // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
237      //   lvalue, [...]
238      // Not so in C.
239    case UO_PreInc:
240    case UO_PreDec:
241      return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
242
243    default:
244      return Cl::CL_PRValue;
245    }
246
247  case Expr::OpaqueValueExprClass:
248    return ClassifyExprValueKind(Lang, E, E->getValueKind());
249
250    // Pseudo-object expressions can produce l-values with reference magic.
251  case Expr::PseudoObjectExprClass:
252    return ClassifyExprValueKind(Lang, E,
253                                 cast<PseudoObjectExpr>(E)->getValueKind());
254
255    // Implicit casts are lvalues if they're lvalue casts. Other than that, we
256    // only specifically record class temporaries.
257  case Expr::ImplicitCastExprClass:
258    return ClassifyExprValueKind(Lang, E, E->getValueKind());
259
260    // C++ [expr.prim.general]p4: The presence of parentheses does not affect
261    //   whether the expression is an lvalue.
262  case Expr::ParenExprClass:
263    return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
264
265    // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
266    // or a void expression if its result expression is, respectively, an
267    // lvalue, a function designator, or a void expression.
268  case Expr::GenericSelectionExprClass:
269    if (cast<GenericSelectionExpr>(E)->isResultDependent())
270      return Cl::CL_PRValue;
271    return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
272
273  case Expr::BinaryOperatorClass:
274  case Expr::CompoundAssignOperatorClass:
275    // C doesn't have any binary expressions that are lvalues.
276    if (Lang.CPlusPlus)
277      return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
278    return Cl::CL_PRValue;
279
280  case Expr::CallExprClass:
281  case Expr::CXXOperatorCallExprClass:
282  case Expr::CXXMemberCallExprClass:
283  case Expr::UserDefinedLiteralClass:
284  case Expr::CUDAKernelCallExprClass:
285    return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType());
286
287    // __builtin_choose_expr is equivalent to the chosen expression.
288  case Expr::ChooseExprClass:
289    return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
290
291    // Extended vector element access is an lvalue unless there are duplicates
292    // in the shuffle expression.
293  case Expr::ExtVectorElementExprClass:
294    if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
295      return Cl::CL_DuplicateVectorComponents;
296    if (cast<ExtVectorElementExpr>(E)->isArrow())
297      return Cl::CL_LValue;
298    return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
299
300    // Simply look at the actual default argument.
301  case Expr::CXXDefaultArgExprClass:
302    return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
303
304    // Same idea for default initializers.
305  case Expr::CXXDefaultInitExprClass:
306    return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
307
308    // Same idea for temporary binding.
309  case Expr::CXXBindTemporaryExprClass:
310    return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
311
312    // And the cleanups guard.
313  case Expr::ExprWithCleanupsClass:
314    return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
315
316    // Casts depend completely on the target type. All casts work the same.
317  case Expr::CStyleCastExprClass:
318  case Expr::CXXFunctionalCastExprClass:
319  case Expr::CXXStaticCastExprClass:
320  case Expr::CXXDynamicCastExprClass:
321  case Expr::CXXReinterpretCastExprClass:
322  case Expr::CXXConstCastExprClass:
323  case Expr::ObjCBridgedCastExprClass:
324    // Only in C++ can casts be interesting at all.
325    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
326    return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
327
328  case Expr::CXXUnresolvedConstructExprClass:
329    return ClassifyUnnamed(Ctx,
330                      cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
331
332  case Expr::BinaryConditionalOperatorClass: {
333    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
334    const BinaryConditionalOperator *co = cast<BinaryConditionalOperator>(E);
335    return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
336  }
337
338  case Expr::ConditionalOperatorClass: {
339    // Once again, only C++ is interesting.
340    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
341    const ConditionalOperator *co = cast<ConditionalOperator>(E);
342    return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
343  }
344
345    // ObjC message sends are effectively function calls, if the target function
346    // is known.
347  case Expr::ObjCMessageExprClass:
348    if (const ObjCMethodDecl *Method =
349          cast<ObjCMessageExpr>(E)->getMethodDecl()) {
350      Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getResultType());
351      return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
352    }
353    return Cl::CL_PRValue;
354
355    // Some C++ expressions are always class temporaries.
356  case Expr::CXXConstructExprClass:
357  case Expr::CXXTemporaryObjectExprClass:
358  case Expr::LambdaExprClass:
359  case Expr::CXXStdInitializerListExprClass:
360    return Cl::CL_ClassTemporary;
361
362  case Expr::VAArgExprClass:
363    return ClassifyUnnamed(Ctx, E->getType());
364
365  case Expr::DesignatedInitExprClass:
366    return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
367
368  case Expr::StmtExprClass: {
369    const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
370    if (const Expr *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
371      return ClassifyUnnamed(Ctx, LastExpr->getType());
372    return Cl::CL_PRValue;
373  }
374
375  case Expr::CXXUuidofExprClass:
376    return Cl::CL_LValue;
377
378  case Expr::PackExpansionExprClass:
379    return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
380
381  case Expr::MaterializeTemporaryExprClass:
382    return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
383              ? Cl::CL_LValue
384              : Cl::CL_XValue;
385
386  case Expr::InitListExprClass:
387    // An init list can be an lvalue if it is bound to a reference and
388    // contains only one element. In that case, we look at that element
389    // for an exact classification. Init list creation takes care of the
390    // value kind for us, so we only need to fine-tune.
391    if (E->isRValue())
392      return ClassifyExprValueKind(Lang, E, E->getValueKind());
393    assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
394           "Only 1-element init lists can be glvalues.");
395    return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
396  }
397
398  llvm_unreachable("unhandled expression kind in classification");
399}
400
401/// ClassifyDecl - Return the classification of an expression referencing the
402/// given declaration.
403static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
404  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
405  //   function, variable, or data member and a prvalue otherwise.
406  // In C, functions are not lvalues.
407  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
408  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
409  // special-case this.
410
411  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
412    return Cl::CL_MemberFunction;
413
414  bool islvalue;
415  if (const NonTypeTemplateParmDecl *NTTParm =
416        dyn_cast<NonTypeTemplateParmDecl>(D))
417    islvalue = NTTParm->getType()->isReferenceType();
418  else
419    islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
420	  isa<IndirectFieldDecl>(D) ||
421      (Ctx.getLangOpts().CPlusPlus &&
422        (isa<FunctionDecl>(D) || isa<FunctionTemplateDecl>(D)));
423
424  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
425}
426
427/// ClassifyUnnamed - Return the classification of an expression yielding an
428/// unnamed value of the given type. This applies in particular to function
429/// calls and casts.
430static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
431  // In C, function calls are always rvalues.
432  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
433
434  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
435  //   lvalue reference type or an rvalue reference to function type, an xvalue
436  //   if the result type is an rvalue reference to object type, and a prvalue
437  //   otherwise.
438  if (T->isLValueReferenceType())
439    return Cl::CL_LValue;
440  const RValueReferenceType *RV = T->getAs<RValueReferenceType>();
441  if (!RV) // Could still be a class temporary, though.
442    return ClassifyTemporary(T);
443
444  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
445}
446
447static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
448  if (E->getType() == Ctx.UnknownAnyTy)
449    return (isa<FunctionDecl>(E->getMemberDecl())
450              ? Cl::CL_PRValue : Cl::CL_LValue);
451
452  // Handle C first, it's easier.
453  if (!Ctx.getLangOpts().CPlusPlus) {
454    // C99 6.5.2.3p3
455    // For dot access, the expression is an lvalue if the first part is. For
456    // arrow access, it always is an lvalue.
457    if (E->isArrow())
458      return Cl::CL_LValue;
459    // ObjC property accesses are not lvalues, but get special treatment.
460    Expr *Base = E->getBase()->IgnoreParens();
461    if (isa<ObjCPropertyRefExpr>(Base))
462      return Cl::CL_SubObjCPropertySetting;
463    return ClassifyInternal(Ctx, Base);
464  }
465
466  NamedDecl *Member = E->getMemberDecl();
467  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
468  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
469  //   E1.E2 is an lvalue.
470  if (ValueDecl *Value = dyn_cast<ValueDecl>(Member))
471    if (Value->getType()->isReferenceType())
472      return Cl::CL_LValue;
473
474  //   Otherwise, one of the following rules applies.
475  //   -- If E2 is a static member [...] then E1.E2 is an lvalue.
476  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
477    return Cl::CL_LValue;
478
479  //   -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
480  //      E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
481  //      otherwise, it is a prvalue.
482  if (isa<FieldDecl>(Member)) {
483    // *E1 is an lvalue
484    if (E->isArrow())
485      return Cl::CL_LValue;
486    Expr *Base = E->getBase()->IgnoreParenImpCasts();
487    if (isa<ObjCPropertyRefExpr>(Base))
488      return Cl::CL_SubObjCPropertySetting;
489    return ClassifyInternal(Ctx, E->getBase());
490  }
491
492  //   -- If E2 is a [...] member function, [...]
493  //      -- If it refers to a static member function [...], then E1.E2 is an
494  //         lvalue; [...]
495  //      -- Otherwise [...] E1.E2 is a prvalue.
496  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member))
497    return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
498
499  //   -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
500  // So is everything else we haven't handled yet.
501  return Cl::CL_PRValue;
502}
503
504static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
505  assert(Ctx.getLangOpts().CPlusPlus &&
506         "This is only relevant for C++.");
507  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
508  // Except we override this for writes to ObjC properties.
509  if (E->isAssignmentOp())
510    return (E->getLHS()->getObjectKind() == OK_ObjCProperty
511              ? Cl::CL_PRValue : Cl::CL_LValue);
512
513  // C++ [expr.comma]p1: the result is of the same value category as its right
514  //   operand, [...].
515  if (E->getOpcode() == BO_Comma)
516    return ClassifyInternal(Ctx, E->getRHS());
517
518  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
519  //   is a pointer to a data member is of the same value category as its first
520  //   operand.
521  if (E->getOpcode() == BO_PtrMemD)
522    return (E->getType()->isFunctionType() ||
523            E->hasPlaceholderType(BuiltinType::BoundMember))
524             ? Cl::CL_MemberFunction
525             : ClassifyInternal(Ctx, E->getLHS());
526
527  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
528  //   second operand is a pointer to data member and a prvalue otherwise.
529  if (E->getOpcode() == BO_PtrMemI)
530    return (E->getType()->isFunctionType() ||
531            E->hasPlaceholderType(BuiltinType::BoundMember))
532             ? Cl::CL_MemberFunction
533             : Cl::CL_LValue;
534
535  // All other binary operations are prvalues.
536  return Cl::CL_PRValue;
537}
538
539static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
540                                     const Expr *False) {
541  assert(Ctx.getLangOpts().CPlusPlus &&
542         "This is only relevant for C++.");
543
544  // C++ [expr.cond]p2
545  //   If either the second or the third operand has type (cv) void, [...]
546  //   the result [...] is a prvalue.
547  if (True->getType()->isVoidType() || False->getType()->isVoidType())
548    return Cl::CL_PRValue;
549
550  // Note that at this point, we have already performed all conversions
551  // according to [expr.cond]p3.
552  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
553  //   same value category [...], the result is of that [...] value category.
554  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
555  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
556            RCl = ClassifyInternal(Ctx, False);
557  return LCl == RCl ? LCl : Cl::CL_PRValue;
558}
559
560static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
561                                       Cl::Kinds Kind, SourceLocation &Loc) {
562  // As a general rule, we only care about lvalues. But there are some rvalues
563  // for which we want to generate special results.
564  if (Kind == Cl::CL_PRValue) {
565    // For the sake of better diagnostics, we want to specifically recognize
566    // use of the GCC cast-as-lvalue extension.
567    if (const ExplicitCastExpr *CE =
568          dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
569      if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
570        Loc = CE->getExprLoc();
571        return Cl::CM_LValueCast;
572      }
573    }
574  }
575  if (Kind != Cl::CL_LValue)
576    return Cl::CM_RValue;
577
578  // This is the lvalue case.
579  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
580  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
581    return Cl::CM_Function;
582
583  // Assignment to a property in ObjC is an implicit setter access. But a
584  // setter might not exist.
585  if (const ObjCPropertyRefExpr *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
586    if (Expr->isImplicitProperty() && Expr->getImplicitPropertySetter() == 0)
587      return Cl::CM_NoSetterProperty;
588  }
589
590  CanQualType CT = Ctx.getCanonicalType(E->getType());
591  // Const stuff is obviously not modifiable.
592  if (CT.isConstQualified())
593    return Cl::CM_ConstQualified;
594
595  // Arrays are not modifiable, only their elements are.
596  if (CT->isArrayType())
597    return Cl::CM_ArrayType;
598  // Incomplete types are not modifiable.
599  if (CT->isIncompleteType())
600    return Cl::CM_IncompleteType;
601
602  // Records with any const fields (recursively) are not modifiable.
603  if (const RecordType *R = CT->getAs<RecordType>()) {
604    assert((E->getObjectKind() == OK_ObjCProperty ||
605            !Ctx.getLangOpts().CPlusPlus) &&
606           "C++ struct assignment should be resolved by the "
607           "copy assignment operator.");
608    if (R->hasConstFields())
609      return Cl::CM_ConstQualified;
610  }
611
612  return Cl::CM_Modifiable;
613}
614
615Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
616  Classification VC = Classify(Ctx);
617  switch (VC.getKind()) {
618  case Cl::CL_LValue: return LV_Valid;
619  case Cl::CL_XValue: return LV_InvalidExpression;
620  case Cl::CL_Function: return LV_NotObjectType;
621  case Cl::CL_Void: return LV_InvalidExpression;
622  case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
623  case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
624  case Cl::CL_MemberFunction: return LV_MemberFunction;
625  case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
626  case Cl::CL_ClassTemporary: return LV_ClassTemporary;
627  case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
628  case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
629  case Cl::CL_PRValue: return LV_InvalidExpression;
630  }
631  llvm_unreachable("Unhandled kind");
632}
633
634Expr::isModifiableLvalueResult
635Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
636  SourceLocation dummy;
637  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
638  switch (VC.getKind()) {
639  case Cl::CL_LValue: break;
640  case Cl::CL_XValue: return MLV_InvalidExpression;
641  case Cl::CL_Function: return MLV_NotObjectType;
642  case Cl::CL_Void: return MLV_InvalidExpression;
643  case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
644  case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
645  case Cl::CL_MemberFunction: return MLV_MemberFunction;
646  case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
647  case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
648  case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
649  case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
650  case Cl::CL_PRValue:
651    return VC.getModifiable() == Cl::CM_LValueCast ?
652      MLV_LValueCast : MLV_InvalidExpression;
653  }
654  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
655  switch (VC.getModifiable()) {
656  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
657  case Cl::CM_Modifiable: return MLV_Valid;
658  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
659  case Cl::CM_Function: return MLV_NotObjectType;
660  case Cl::CM_LValueCast:
661    llvm_unreachable("CM_LValueCast and CL_LValue don't match");
662  case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
663  case Cl::CM_ConstQualified: return MLV_ConstQualified;
664  case Cl::CM_ArrayType: return MLV_ArrayType;
665  case Cl::CM_IncompleteType: return MLV_IncompleteType;
666  }
667  llvm_unreachable("Unhandled modifiable type");
668}
669